1. Field of the Invention
The present invention relates to a developing apparatus and an image forming apparatus, and more particularly to a developing apparatus and an image forming apparatus using a one-component developer.
2. Description of the Prior Art
Methods for dry development of an electrostatic latent image are roughly grouped into two-component development methods using a toner and a carrier and one-component development methods using a toner but not a carrier. One-component development methods, which do not require a carrier, help make developing apparatus compact and light-weight, and in addition do not require maintenance such as replacement of a carrier. For these reasons, one-component development methods are used in low-speed, small-size copiers and printers, and have recently been becoming increasingly widely used even in medium- and high-speed copiers and printers.
However, one-component development methods have a drawback of suffering from occasional disturbances in the thin toner layer supported on a supporting member, ascribable to changes in ambient conditions such as temperature and humidity. Moreover, one-component development methods, compared with two-component development methods, tend to charge the toner with a smaller amount of electric charge with less even distribution. This sometimes leads to flaws in the obtained image, such as low image density or increased toner adhesion in a non-image area (hereinafter referred to as fogging).
An object of the present invention is to provide a developing apparatus and an image forming apparatus that can form a thin toner layer so stably as not to cause flaws in the obtained image despite changes in ambient conditions.
Another object of the present invention is to provide a developing apparatus and an image forming apparatus that can be used in medium- and high-speed copiers and printers.
To achieve the above objects, according to one aspect of the present invention, a developing apparatus is provided with a developer supporting member with a surface roughness RZ in the range from 3.0 to 5.5 xcexcm and a one-component developer with a bulk density in the range from 0.35 to 0.55 g/ml, and an image is developed by forming a layer of the developer on the developer supporting member. With a developing apparatus structured in this way, it is possible to form a thin toner layer stably on the developer supporting member despite changes in ambient conditions, and to prevent lower image density and increased fogging. In the present specification, surface roughness RZ is given as the average of roughness measured at ten spots as defined in JIS (Japanese Industrial Standards) B0601. On the other hand, bulk density denotes the weight per unit volume (g/ml) of the toner when a predetermined container is filled with it under no load, and thus indicates the flowability of the toner.
According to another aspect of the present invention, an image forming apparatus is provided with an image supporting member, charging means for charging the surface of the image supporting member with electric charge, exposing means for irradiating the charged surface of the image supporting member with light to form an electrostatic latent image, developing means for feeding a developer to the electrostatic latent image to develop an image, and transferring means for transferring the developer on the image supporting member developed by the developing means to a transferred-image member. Used as the developing means here is a developing apparatus as described above. With an image forming apparatus structured in this way, just as described above, it is possible to form a thin toner layer stably on the developer supporting member despite changes in ambient conditions, and to prevent lower image density and increased fogging.